glibc中fork系统调用传参

因为想跟踪下在新建进程时，如何处理新建进程的vruntime，所以跟踪了下fork。

 

以glic-2.17中ARM为例（unicore架构的没找到）,实际上通过寄存器向系统调用传递的参数为：

r7: __NR_clone 120

r0: CLONE_CHILD_SETTID | CLONE_CHILD_CLEARTID | SIGCHLD

r1: NULL

r2: NULL

r3: NULL

r4: &THREAD_SELF->tid

fork()---->__fork()---->__libc_fork()

__libc_fork()---->INLINE_SYSCALL (clone, 5,                                   CLONE_CHILD_SETTID |                                   CLONE_CHILD_CLEARTID |                                   SIGCHLD,                                   NULL, NULL, NULL, &THREAD_SELF->tid)

 

#define INLINE_SYSCALL(name, nr, args...)        ({ unsigned int _sys_result = \
                  INTERNAL_SYSCALL (name, , nr, args);             if (__builtin_expect \
                (INTERNAL_SYSCALL_ERROR_P (_sys_result, ), 0))             {       \       
                __set_errno (INTERNAL_SYSCALL_ERRNO \
                            (_sys_result, )); \       
                _sys_result = (unsigned int) -1;  \       
            }    \       
         (int) _sys_result; })

 

#define INTERNAL_SYSCALL(name, err, nr, args...)   \       
            INTERNAL_SYSCALL_RAW(SYS_ify(name), err, nr, args)

//#define __NR_clone 120
#define SYS_ify(syscall_name)   (__NR_##syscall_name)

 

//err没用使用，也没有传递宏参，第一次见到
# define INTERNAL_SYSCALL_RAW(name, err, nr, args...)           \       
  ({                                                            \       
          register int _a1 asm ("r0"), _nr asm ("r7");          \       
          LOAD_ARGS_##nr (args)                                 \       
          _nr = name;                                           \       
          asm volatile ("swi       0x0     @ syscall " #name    \       
                        : "=r" (_a1)                            \       
                        : "r" (_nr) ASM_ARGS_##nr               \       
                        : "memory");                            \       
    _a1; })                                                                                                        

关于宏INTERAL_SYSCALL_RAW还是满有意思的，写了个函数测试下，真实的看下库如何向系统调用传参：

#define LOAD_ARGS_0()
#define ASM_ARGS_0


#define LOAD_ARGS_1(a1)     int _a1tmp = (int)(a1);     LOAD_ARGS_0 ()     _a1 = _a1tmp;

#define ASM_ARGS_1 ASM_ARGS_0, "r" (_a1)



#define LOAD_ARGS_2(a1, a2)     int _a2tmp = (int)(a2);     LOAD_ARGS_1(a1)     register int _a2 asm ("a2") = _a2tmp;

#define ASM_ARGS_2 ASM_ARGS_1, "r" (_a2)



#define LOAD_ARGS_3(a1, a2, a3)     int _a3tmp = (int)(a3);     LOAD_ARGS_2 (a1, a2)     register int _a3 asm ("a3") = _a3tmp;

#define ASM_ARGS_3 ASM_ARGS_2, "r" (_a3)



#define LOAD_ARGS_4(a1, a2, a3, a4)     int _a4tmp = (int) (a4);     LOAD_ARGS_3 (a1, a2, a3)     register int _a4 asm ("a4") = _a4tmp;

#define ASM_ARGS_4 ASM_ARGS_3, "r" (_a4)



#define LOAD_ARGS_5(a1, a2, a3, a4, a5)     int _v1tmp = (int)(a5);     LOAD_ARGS_4 (a1, a2, a3, a4)     register int _v1 asm ("v1") = _v1tmp; 

#define ASM_ARGS_5 ASM_ARGS_4, "r" (_v1)

#define INTERNAL_SYSCALL_RAW(name, err, nr, args...)     ({         register int _a1 asm("r0"), _nr asm("r7");         LOAD_ARGS_5 (args)         _nr = name;         asm volatile ("swi 0x0"                       : "=r" (_a1)                       : "r" (_nr) ASM_ARGS_##nr                       : "memory"                      );         _a1;      })

void test(void)
{
    INTERNAL_SYSCALL_RAW(120, , 5,  6, 7, 8, 9, 0);
}                                                                                                                  

 

预处理后即为：

void test(void)                                                                                                    
{
 ({ 
      register int _a1 asm("r0"), _nr asm("r7"); 
      int _v1tmp = (int)(0); 
      int _a4tmp = (int) (9); 
      int _a3tmp = (int)(8); 
      int _a2tmp = (int)(7); 
      int _a1tmp = (int)(6); 
      _a1 = _a1tmp; 
      register int _a2 asm ("a2") = _a2tmp; 
      register int _a3 asm ("a3") = _a3tmp; 
      register int _a4 asm ("a4") = _a4tmp; 
      register int _v1 asm ("v1") = _v1tmp; 
      _nr = 120;  
      asm volatile (
                      "swi 0x0" 
                      : "=r" (_a1) 
                      : "r" (_nr) , "r" (_a1), "r" (_a2),
                        "r" (_a3), "r" (_a4), "r" (_v1) 
                      : "memory" 
                  );      
      _a1;    
    });
}

相应的汇编代码：

test:                                                                                                              
    stmfd   sp!, {r4, r7, fp}
    add fp, sp, #8
    sub sp, sp, #28

    mov r3, #0
    str r3, [fp, #-32]

    mov r3, #9
    str r3, [fp, #-28]

    mov r3, #8
    str r3, [fp, #-24]

    mov r3, #7
    str r3, [fp, #-20]

    mov r3, #6
    str r3, [fp, #-16]

    ldr r0, [fp, #-16]
    ldr r1, [fp, #-20]
    ldr r2, [fp, #-24]
    ldr r3, [fp, #-28]
    ldr r4, [fp, #-32]
    mov r7, #120
#APP
@ 16 "go.c" 1
    swi 0x0
@ 0 "" 2
    sub sp, fp, #8
    ldmfd   sp!, {r4, r7, fp}
    bx  lr